This article explores Jeffrey Rosen’s depiction of Justice Brandeis as a “Jeffersonian prophet,” “the leader of a Jeffersonian tradition,” and “the Jewish Jefferson” to examine the meaning of the term “libertarian” in the context of American constitutional jurisprudence. It argues that Rosen unsettles the characterization of Brandeis as non-libertarian or anti-libertarian and, consequently, destabilizes the very meaning of “libertarianism” as that term is used by self-described libertarians in current scholarship about American constitutionalism. Whether Brandeis was a pure or true libertarian does not concern me. What interests me is the way in which scholars have invoked Brandeis to delimit the nature of libertarian jurisprudence in the American constitutional context. Brandeis simultaneously illuminates and problematizes the designation “libertarian.” His formative influence on American constitutional law elicits dogged attempts to categorize or classify him. He continues to attract admirers and provoke antagonists, both of whom express firm opinions about his association with libertarianism. At stake in the debate over Brandeis’s association with libertarianism is the meaning and import of “libertarian” jurisprudence in our constitutional tradition. Disturbing any consensus regarding the term “libertarian” in the context of American constitutional jurisprudence is significant because it necessitates two questions: what, exactly, is “libertarian” jurisprudence, and who decides? Answers to these questions may disrupt the momentum that self-identified libertarian legal scholars have enjoyed over the last decade and underscore claims to libertarianism that are at odds with that consensus.